Different implantable medical devices have been developed for treating various ailments associated with body lumens, such as ailments of body vessel walls or other lumenal walls. One category of implantable medical device that has been developed for artificial occlusion of body spaces is the category of "artificial occlusion devices." Although artificial occlusion devices are useful in occluding body spaces, other applications include occluding body lumens. Examples of lumens that have been identified as candidates for treatment with artificial occlusion devices include, for example, the vas deferens or the fallopian tubes. Most commonly, however, artificial occlusion devices have been disclosed for medical treatment of the vascular lumens and aneurysms in the walls of such vessels. This treatment is commonly referred to as "artificial vaso-occlusion."
Artificial Vaso-occlusion
Artificial vaso-occlusion is a medical treatment that has involved techniques such as the delivery of various occlusive agents including solidifying suspensions, thrombogenic fluids, or emboli such as hog hair or suspensions of metal particles. Delivery of such agents or emboli normally causes a thrombogenic or other occlusive tissue response. Recent advancements in artificial occlusion of vessels and aneurysms have included the delivery and implantation of metal coils. Implantable metal coils that are useful as artificial occlusion devices in vascular lumens or aneurysms are herein referred to as "vaso-occlusion coils."
Vaso-occlusion coils generally are constructed of a wire, usually made of a metal or metal alloy, that is wound into a helix. Vaso-occlusion coils are normally delivered through microcatheters such as the type disclosed in U.S. Pat. No. 4,739,768 to Engelson. The microcatheter commonly tracks a guide wire to a point just proximal of or within the desired site for occlusion. The coil is advanced through the microcatheter and out the distal end hole so to at least partially fill the selected space and create an occlusion.
Once a vaso-occlusion coil is implanted at a desired site, occlusion results either from the space-filling mechanism inherent in the coil itself, or from a cellular response to the coil such as a thrombus formation, or both. The space-filling mechanism of the vaso-occlusion coil may be either based upon a pre-determined secondary geometry, or may be based upon random flow characteristics of the coil as it is expelled from a delivery sheath lumen.
Vaso-occlusion coils have been disclosed that have a secondary geometry or shape which dictates at least in part their space-filling occlusion mechanism. Such a secondary shape may include a secondary helical structure which involves the primary coil helix being itself wound into a second helix. In addition to the space-filling feature, another benefit to having a secondary coil shape is that it may allow the coil readily to anchor itself against the walls of a delivery site. For example, a vaso-occlusion coil having a secondary shape may be ejected from a sheath lumen where it was constrained in a stretched condition to have a first outer diameter equal to the sheath lumen inner diameter. When ejected, the coil passively expands to its secondary shape, often having a larger, second outer diameter to aid in space-filling the body cavity or lumen. This may be an expansion to the coil's relaxed, unrestrained memory state--or at least until the coil encounters a vessel wall against which it exerts a force to complete the anchoring process.
One example of a type of vaso-occlusion coil having a pre-determined secondary shape is described in U.S. Pat. No. 4,994,069 to Ritchart et al. Ritchart describes a vaso-occlusive wire having a memory imparted thereto by heating the wire at about 800.degree. F. for 24 hours after it is shaped. This memory is effective to return the wire from a stretched, linear condition in which it is advanced through a catheter to a space-filling relaxed condition as the wire is released from the catheter. The diameter of the secondary shape is approximately equal to and may be larger than the vessel in which it is deployed.
In contrast to vaso-occlusion coils having pre-determined secondary shapes that dictate in part their space-filling mechanism, other vaso-occlusion coils have been disclosed that take on random shapes when expelled from a delivery sheath. This type of vaso-occlusive coil is often referred to as the "liquid coil." One example of such a vaso-occlusive coil which takes on a random occlusive shape when delivered into a body space is disclosed in pending U.S. patent application Ser. No. 08/413,970, filed Mar. 30, 1995. This document describes very soft and flexible coils which are flow-injectable through the delivery catheter using, e.g., saline solution.
In addition to the various types of space-filling mechanisms and geometries of vaso-occlusion coils, other particularized features of coil designs, such as mechanisms for delivering vaso-occlusion coils through delivery catheters and implanting them in a desired occlusion site, have also been described. Examples of categories of vaso-occlusion coils based upon their delivery mechanisms include pushable coils, mechanically detachable coils, and electrolytically detachable coils.
One example of the type of vaso-occlusion coil referred to as the "pushable coil" is disclosed in U.S. Pat. No. 4,994,069 to Ritchart et al., introduced above. Pushable coils are commonly provided in a cartridge and are pushed or "plunged" from the cartridge into a delivery catheter lumen. A pusher rod advances the pushable coil through and out of the delivery catheter lumen and into the site for occlusion.
In contrast to pushable coils, mechanically detachable vaso-occlusion coils are integrated with a pusher rod and mechanically detached from the pusher after exiting a delivery catheter. Examples of such mechanically detachable vaso-occlusion coils are provided in U.S. Pat. No. 5,261,916 to Engelson, or U.S. Pat. No. 5,250,071 to Palermo.
Further in contrast to the mechanically detachable type of vaso-occlusion coil, the electrolytically detachable type is also integrated with a pusher rod, but is detached from the pusher by applying a direct current that dissolves a sacrificial link between the pusher and the coil. Examples of such electrolytically detachable vaso-occlusion coils are disclosed in U.S. Pat. No. 5,122,136 to Guglielmi, et al, and U.S. Pat. No. 5,354,295 to Guglielmi, et al.
A further improvement upon the electrolytic detachment mechanisms just previously referenced is disclosed in pending U.S. patent application Ser. No. 08/205,512, filed Mar. 3, 1994. This document describes superimposing an alternating current signal over the direct current signal, wherein a sensing circuit monitors the alternating current signal as an indicator of the progression of coil detachment.
Improvements for enhancing the thrombogenic or other occlusive tissue response to metal coils have also been disclosed. For example, vaso-occlusion coils having vaso-occlusive fibers attached thereto have been described (see for example, U.S. Pat. No. 5,226,911 to Chee et al.). A further type of vaso-occlusion coil is used as a detachable dielectric electrode in a radio-frequency artificial vaso-occlusion system, as disclosed in pending U.S. patent application Ser. No. 08/497,507, filed Jun. 30, 1995.
The disclosures of the various patent and pending patent application documents identified in the preceding paragraphs are herein incorporated in their entirety by reference.
Vaso-occlusion Coils in Aneurysms
A wide variety of clinical abnormalities in body lumens may be treated with artificial occlusion methods. For example, artificial occlusion methods have been disclosed for treating feeder vessels into tumors, arterio-venous malformations, fistulas, and aneurysms of vessel walls. Among arterial abnormalities, aneurysms present particular medical risk due to the dangers of potential rupture of the thinned wall inherent in an aneurysm. Occlusion of aneurysms with vaso-occlusion coils without occluding the adjacent artery is a desirable method of reducing such risk.
In one disclosed method of treating aneurysms with vaso-occlusion coils, a microcatheter is initially steered into or adjacent the entrance of an aneurysm, aided by a steerable wire. The wire is then withdrawn from the microcatheter lumen and replaced by the vaso-occlusion coil. The vaso-occlusion coil is advanced through and out of the microcatheter, desirably being completely delivered into the aneurysm. After or during delivery of such a coil into the aneurysm, a portion of the coil might then migrate out of the aneurysm entrance zone and into the feeding vessel. This may cause an undesirable response of occluding the feeding vessel. Also, there is an additional risk that the blood flow may induce movement of the coil farther out of the aneurysm, resulting in a more developed embolus in the good vessel.
One type of aneurysm, commonly referred to as a "wide-neck aneurysm," is known to present particular difficulty in placing and retaining vaso-occlusion coils. Wide-neck aneurysms are herein referred to as aneurysms of vessel walls having a neck or "entrance zone" from the adjacent vessel, which entrance zone has a diameter that either: (1) is at least 80% of the largest diameter of the aneurysm; or (2) is clinically observed to be too wide to effectively retain vaso-occlusion coils that are deployed using conventional techniques.
In attempting to prevent potential migration of vaso-occlusion coils from aneurysms, catheter distal tip shapes may be formed on delivery microcatheters to help support the distal tip during deployment of vaso-occlusive agents. However, this may provide only a partial solution, particularly in the case of wide-neck aneurysms.
There is a need for a retaining device that is adapted to block an entrance zone to an aneurysm such that occlusion devices may be implanted in and retained within the aneurysm and are prevented from migrating through the entrance zone of the aneurysm and into the adjacent vessel.